Adaptive controller with mode tracking and parametric estimation for digital power converters

ABSTRACT

A controller for a power stage may adaptively control power switches to improve the efficiency of power consumption by the power stage and detect continuous conduction mode (“CCM”) and discontinuous conduction mode (“DCM”) operations of the power stage without instantaneous or cycle by cycle sensing and sampling of the output inductor current. Additionally, the controller may be used to facilitate the estimation of output inductor value, the peak inductor current value, and other information on converter operations.

RELATED APPLICATION

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 11/710,101, filed Feb. 23, 2007, entitled “AdaptiveController with Mode Tracking and Parametric Estimation for DigitalPower Converters”, to be issued as U.S. Pat. No. 7,652,459, the entirecontents of which are hereby incorporated by reference.

BACKGROUND

1. Field

This disclosure relates generally to power delivery technologies in anelectronic system, and more specifically but not exclusively, tocontrollers for power converters in an electronic system.

2. Description

As Integrated Circuits (“ICs”) (e.g., Digital Signal Processors(“DSPs”)) Circuits) in a computing platform become more power efficient,it is naturally desirable that a voltage regulator (“VR”) or a powerdelivery subsystem for such ICs becomes more energy efficient duringpower conversion at all load levels including light loads. Variableswitching frequency combined with Discontinuous Conduction Mode (DCM) isused to improve converter efficiency at light loads. Such schemes mayresult in improved light load efficiency with no impact on high loadefficiency but sometimes at the expense of degraded performance in termsof steady-state voltage ripple and dynamics. Other schemes such asnon-linear control schemes are also proposed to meet the demand onperformances while improving light load efficiency, but requireadditional detection of the peak inductor current in DCM.

Typically, a digital controller is used to control power deliverysubsystem and to interface with ICs and other components in a digitalsystem. A digital controller has advantages for being flexible andgenerally resulting in higher power conversion efficiency at all loadslevels than an analog controller. For a typical digital controller toperform well, however, it requires the detection of DCM, which furtherrequires sensing the output inductor current and detecting thezero-crossing point of the output inductor current. To accurately detectthe zero-crossing point of the output inductor current, the outputinductor current needs to be sampled at a high sampling rate, to beconverted to the digital form, and to be compared with zero. This meanshigh speed sampling, high resolution analog-to-digital conversion(“ADC”), and high speed comparison are required. All of these result inan increase in power consumption, and in the size and cost of the powerdelivery subsystem and the entire system. Moreover, the switching noise,which is introduced at instances of turning on and off of the converterswitches (when the zero crossing and peak of inductor current occurs),makes it more difficult to detect the zero-crossing point of the outputinductor current. Furthermore, the addition of the sensing circuit forthe output inductor current may impact the accuracy of the sensed andsampled values of the output inductor current and may in turn impact theoperation accuracy of the digital power converter.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the disclosed subject matter will becomeapparent from the following detailed description of the subject matterin which:

FIG. 1 illustrates a diagram of a power converter with a digitalcontroller;

FIG. 2 illustrates a diagram of a power converter with a digitalcontroller, according to an embodiment of the subject matter disclosedin the present application;

FIGS. 3A and 3B illustrate the output inductor current waveforms ofpower converter 200 (as shown in FIG. 2) operated in continuousconduction mode (“CCM”) and in discontinuous conduction mode (“DCM”),respectively;

FIG. 4 is a flowchart of one example process for adaptively controlpower switches without sensing the output inductor current, according toan embodiment of the subject matter disclosed in the presentapplication;

FIG. 5 illustrates the relationship between the duty cycle of the lowerswitch in a digital power converter and the zero-crossing of the outputinductor current;

FIG. 6 is a schematic illustrating a method for determining theoperation mode of a power converter, according to an embodiment of thesubject matter disclosed in the present application; and

FIG. 7 is a flowchart of one example process for tracking the peakoutput inductor current in DCM and to control the output voltage rippleby limit the peak output inductor current in DCM.

DETAILED DESCRIPTION

According to embodiments of the subject matter disclosed in thisapplication, a digital controller for a power converter may adaptivelycontrol power switches and detect continuous conduction mode (“CCM”) anddiscontinuous conduction mode (“DCM”) operations of the power converterwithout instantaneous or cycle by cycle sensing and sampling of theoutput inductor current. This may result in savings of power consumptionby and the size and cost of a power converter in an electronic system.Additionally, the digital controller may be used to facilitate theestimation of output inductor value, the peak inductor current value,and other information on converter operations based in part on the inputcurrent obtained via low speed sensing.

Reference in the specification to “one embodiment” or “an embodiment” ofthe disclosed subject matter means that a particular feature, structureor characteristic described in connection with the embodiment isincluded in at least one embodiment of the disclosed subject matter.Thus, the appearances of the phrase “in one embodiment” appearing invarious places throughout the specification are not necessarily allreferring to the same embodiment.

FIG. 1 illustrates a diagram of a power converter 100 with a digitalcontroller 140. Power converter 100 includes a control power switch 110,a synchronous power switch 115, a gate driver 120 to power switches 110and 115, an output inductor 130, an output capacitor 160 of the powerconverter 100, a load 165 of the power converter, and an input powersource 105 which supplies input voltage and/or power to the powerconverter. When control power switch 110 is turned on, the input powersource 105 forces current into output inductor 130 and charges outputcapacitor 160. When the current in output inductor reaches its highpeak, control power switch 110 is turned off and synchronous powerswitch 115 is turned on to provide a closed path for the output inductorcurrent to flow. When the output inductor current decreases to its lowerpeak, synchronous power switch 115 is turned off and control powerswitch 110 is turned on. In most applications, the output inductorcurrent never drops to zero at during full-load operation (this isdefined as continuous conduction mode (“CCM”) operation). Overallperformance is usually better using CCM, and it allows maximum outputpower to be obtained from a given input voltage and switch currentrating.

In applications where the maximum load current is fairly low, the outputinductor current may drop to zero. When this happens, it can beadvantageous to operate the power converter 100 in a design fordiscontinuous conduction mode (“DCM”), that is, when the output inductorcurrent drops to zero, synchronous power switch 115 is turned off toprevent the output inductor current drops below zero before controlpower switch 110 is turned on again. Operating in discontinuous mode mayresult in a smaller overall converter size because a smaller inductormay be used. Operating at DCM at lower load current values is generallyharmless and even converters designed for CCM operations at full loadwill become discontinuous as the load current is decreased. FIGS. 3A and3B show waveforms of the output inductor current, i_(L), in CCM and DCM,respectively.

Additionally, the power converter 100 includes a digital controller 140,a fast analog-to-digital converter (“ADC”) 155, one or more slow ADC125, and a gate driver 120. Digital controller 140 may include anadvanced control scheme unit 145, a comparator 170, and some othercomponents. Although not shown in the figure, the power converter 100also includes a sensing component to sense the output inductor currentand feed the sensed inductor current to fast ADC 155, and other sensingcomponents to sense other data such as the input current. Fast ADC 155converts the sensed inductor current from analog to digital form. Thedigitized inductor current may be first amplified/compensated before itis provided to comparator 170 in digital controller 140. The comparator170 compares the digitized inductor current with zero to detect thezero-crossing point of the inductor current. To improve the accuracy ofthe zero-crossing detection, it is desirable that ADC 155 be fast withhigh resolution and that comparator 170 also be fast. Slow ADC 125 mayconvert other sensed data such as input current from analog form todigital form and provides the digitized data to digital controller 140.

Digital controller 140 receives digitized data such as input current andoutput inductor current, process such data, and based on the processedresults determines through advanced control scheme unit 145 what controlsignal it should send to gate driver 120. Based on the control signalreceived from the digital controller, gate driver 120 generates acontrol signal 175 for control power switch 110 and a control signal 180for synchronous power switch 115. When the power converter operates inCCM, control signal 175 and control signal 180 may be complementary toeach other, i.e., when control signal 175 is high (i.e., control powerswitch 110 is turned on), control signal 180 is low (i.e., switch 115 isturned off); and when control signal 175 is low (switch 110 is turnedoff), control signal 180 is high (switch 115 is turned on). When thepower converter operates in DCM, the switching frequency of controlsignal 175 may remains the same or similar to that under CCM; but theswitching frequency of control signal 180 will vary. Under DCM, digitalcontroller detects the point where the output inductor current iscrossing zero and turns control signal 180 to low through gate driver120 even though control signal 175 still remains low. Example waveformsof control signal 175 and control signal 180 are shown in FIG. 6 wherewaveform 610 illustrates control signal 175 under both CCM and DCM;waveform 620 illustrates control signal 180 under CCM; and waveform 630illustrates control signal 180 under DCM.

For power converter 100 to operate in DCM properly, ADC 155 needs to befast with high resolution, and comparator 170 needs to be fast also. Forexample, for a power converter operating at 500 kHz, a sensing componentfor the output inductor current with a bandwidth of larger than 10 MHzis necessary to maintain a proper operation (sensing of actual and notdistorted inductor current signal). If this signal is instantaneouslysampled cycle by cycle, an ADC of 12-bit with 5M samples/second orhigher resolution is necessary. Such circuits will provide thecontroller with information such as peak current and zero crossing/modeinformation at the expense of increase of power consumption, cost, size,and design complexity. In addition, the inductor value in a powerconverter cannot be measured or calculated without additional circuitry.

FIG. 2 illustrates a diagram of a power converter 200 with a digitalcontroller 240, according to an embodiment of the subject matterdisclosed in the present application. Power converter 200 includes acontrol power switch 210, a synchronous power switch 215, a DCM/CCMcapable driver 220 for power switches 210 and 215, an output inductor230, an output capacitor 260 of the power converter 200, a load 265 ofthe power converter, and an input power source 205 which supplies inputvoltage and/or power to the power converter. These components of powerconverter 200 correspond to those components in power converter 100shown in FIG. 1 (e.g., DCM/CCM capable driver 220 corresponds to gatedriver 120 in FIG. 1).

Differences between power converter 200 and power converter 100 includebut not limited to 1) there is no sensing of output inductor current inpower converter 200; 2) no high speed/high resolution ADC is required inpower converter 200; 3) there is no high speed comparator is necessaryin power converter 200; and 4) no need to detect peaks of outputinductor current in power converter 200. The only sensed information inaddition to the output voltage 250 for regulation is the average inputcurrent 235. Neither the output voltage 250 nor the average inputcurrent 235 requires high-speed sensing or high speed/high resolutionADC. Based on the digitized output voltage and the digitized averageinput current, digital controller 240 of power converter 200 detects thezero-crossing point of the output inductor current using an advancedcontrol scheme as illustrated in FIGS. 4 and 5; and generates a controlsignal to DCM/CCM capable driver 220 accordingly. DCM/CCM capable driver220 may produce control signal 275 for control power switch 210 andcontrol signal 280 for synchronous power switch 215. When powerconverter 200 operates in DCM, control signal 280 turns to low (evenwhen control signal 275 still remains low) when the zero-crossing pointof the output inductor current is detected by digital controller 240.Additionally, digital controller 240 may determine whether powerconverter 200 operates under CCM or DCM based on control signal 275 andcontrol signal 280. Furthermore, digital controller 240 may be able toestimate parameters such as DCM peak inductor current, output inductorvalue, and critical input current.

FIGS. 3A and 3B illustrate the output inductor current waveforms ofpower converter 200 (as shown in FIG. 2) operated in CCM and in DCM,respectively. Since a digital controller 240 is used, the duty cycle (D)of the control power switch 210 is available with no required sensing.By utilizing the knowledge of the sensed input current I_(in) and D,converter parameters may be estimated more accurately, since these twoparameters are directly related to (or impacted by) the effect of powerlosses of a converter. The duty cycle (D₁) of the synchronous powerswitch 215 depends on the operation mode, CCM or DCM. In CCM,D_(1-CCM)≈1−D_(CCM); while in DCM, D_(1-DCM) value depends on theinductor current zero crossing point, which is a function of many powerconverter design parameters. As shown in FIGS. 3A and 3B, D_(CCM) standsfor the duty cycle of the “on” time of the synchronous power switch inCCM; D_(1-CCM) stands for the duty cycle of the “off” time of thesynchronous power switch in CCM; D_(1-DCM) stands for the duty cycle ofthe “on” time of the synchronous power switch in DCM; and D_(DCM) standsfor the duty cycle of the “off” time of the synchronous power switchthat corresponds to the rising edge of the output inductor current.These duty cycles may be estimated using the equations below.

CCM Mode:

D _(CCM) ≈V _(o) /V _(in)  (1)

D _(1-CCM)≈1−(V _(o) /V _(in))=1−D _(CCM)  (2)

DCM Mode:

$\begin{matrix}{D_{DCM} \approx {D_{1 - {DCM}} \cdot \left\lbrack {V_{o}/\left( {V_{in} - V_{o}} \right)} \right\rbrack} \approx \sqrt{\begin{bmatrix}{\begin{pmatrix}{2 \cdot L_{o} \cdot I_{o} \cdot} \\{V_{o} \cdot f_{s - {DCM}}}\end{pmatrix}/} \\\left( {V_{in} \cdot \left( {V_{in} - V_{o}} \right)} \right)\end{bmatrix}}} & (3) \\{D_{1 - {DCM}} \approx {\sqrt{\begin{bmatrix}{\begin{pmatrix}{2 \cdot L_{o} \cdot I_{o} \cdot} \\f_{s - {DCM}}\end{pmatrix}/} \\\left( {V_{in} - V_{o}} \right)\end{bmatrix}} \cdot \left( {\sqrt{V_{in}/V_{o}} - \sqrt{V_{o}/V_{in}}} \right)}} & (4)\end{matrix}$

In the above equations, V_(o) is the output voltage of the powerconverter; I_(o) is the output load current; L_(o) is the inductance ofthe output inductor; f_(s-DCM) is the switching frequency of thesynchronous power switch in DCM. In practice, in order to have a moreaccurate value for D_(1-CCM),

$\frac{\left( {t_{df} + t_{dr}} \right)}{T_{s - {CCM}}}$

may be subtracted from D_(1-CCM) in Equation (2), where t_(df) andt_(dr), are the minimum values of falling and rising edges dead-timesbetween the control power switch and the synchronous power switch inorder to prevent the overlapping.

The duty cycle D is controlled by the closed loop feedbackcompensation/controller. D₁ varies in DCM and CCM and needs to be found.In fact, tracking D₁ is equivalent to detecting the zero-crossinginstant 350 (as shown in FIG. 3B) of the output inductor current. FIG. 4is a flowchart of one example process 400 for adaptively control powerswitches by tracking the duty cycle of the synchronous power switchoperating in DCM without sensing the output inductor current, accordingto an embodiment of the subject matter disclosed in the presentapplication. Based on the assumption that the optimum D₁ value existswhich is close to the value of 1−D in CCM and close to the inductor zerocrossing point in DCM, D₁ is varied (incremented and decremented), asillustrated in FIG. 5, until the minimum input current is achieved. Whenthe input current is the minimum, it indicates that the minimum power isconsumed. Thus, the value of D₁ that corresponds to the minimum inputcurrent represents the optimum value of D₁.

Process 400 starts at block 405. At block 410, the value of the inputcurrent may be obtained from a sensing component in the power converter.At block 415, the value change of the input current, ΔI_(in), may becalculated in response to the value change of D₁, ΔD₁ (increase ordecrease), from a previous sampling point to the current sampling point.At block 420, the current sampling values of the input current and D₁may be saved as their corresponding previous sampling values as thesampling process will move to the next sampling point (i.e., the nextsampling point will become the current sampling point). At block 425,the sign of ΔI_(in) and the sign of ΔD₁ may be compared. If they are thesame, a further determination at block 430 may be performed. If the signof ΔI_(in) and the sign of ΔD₁ are not the same, a further determinationat block 435 may be performed. At block 430, the current value of D₁ iscompared with the value of 1−(D+(t_(df)+t_(dr))/T_(s-CCM)). If theformer is not less than the later, this indicated that the powerconverter may operate in CCM and process 400 thus moves to block 450 towait for a number of switching cycles to start the process again. If thevalue of D₁ is less than the value of 1−(D+(t_(df)+t_(dr))/T_(s-CCM)),it indicates that the power converter operates in DCM and the optimalpoint of D₁ has not been reached; and the sampling point of D₁ may moveforward by one step at block 440. At block 435, current value of D₁ iscompared with the value of t_(df)/T_(s-CCM) (this may be considered asthe minimum value for D₁). If D₁ is not larger than t_(df)/T_(s-CCM),process 400 moves to block 450 to wait for a number of switching cyclesto restart the process again. If D₁ is larger than t_(df)/T_(s-CCM), thesampling point of D₁ may move backward by one step at block 445. Ingeneral, when there is more than a certain number, say two, ofconsecutive increment and decrement about the optimum point, process 400may be stopped and D₁ can be set until an input current change occurs.The optimal value of D₁ may be stored along with its associated I_(in)so that it can be utilized in further parameters estimation and/or beused as a starting point for the next search for the optimal D₁.

FIG. 5 illustrates the relationship between the duty cycle of the lowerswitch in a digital power converter and the zero-crossing of the outputinductor current. As shown in the figure, there is one point ofD₁(optimum D₁ 510) which corresponds to the minimum value of I_(in).Since the input voltage is normally fixed, the minimum I_(in)corresponds to the highest power consumption efficiency. Using therelationship of D₁ and I_(in) as shown in this figure, the optimum D₁may be found according to the process as shown in FIG. 4. It should benoted that if the input voltage is not fixed, the input power ratherthan the input current should be used to search for the optimum D₁,which should corresponds to the minimum input power.

The duty cycle of control power switch (e.g., 210 in FIG. 2) and theduty cycle of synchronous power switch (e.g., 215 in FIG. 2) may be usedto determine whether the current operation mode of the power converteris CCM or DCM. One way for making such a determination is as follows:

$\begin{matrix}\left\{ \begin{matrix}{{1 - D} > D_{1}} & \left. \Rightarrow{DCM} \right. \\{Otherwise} & \left. \Rightarrow{CCM} \right.\end{matrix} \right. & (5)\end{matrix}$

Another way for making such a determination is illustrated in FIG. 6.When the power converter (e.g., 200 in FIG. 2) operates in CCM, thecontrol signal for control power switch and the control signal forsynchronous power switch are complimentary as illustrated by waveform610 and 620 in FIG. 6 (i.e., when 610 is high, 620 is low; and viceversa). When the power converter operates in DCM, however, there is agap (shown as 690 in FIG. 6) between the instant when synchronous powerswitch is turned off and the instant when control power switch is turnedon (the control signal for synchronous power switch operating in DCM isillustrated by waveform 630 in FIG. 6). Thus, if an logic OR operationis performed between the control signal for control power switch and thecontrol signal for synchronous power switch, the output will ideally bealways high as illustrated by waveform 670 in CCM and will be low duringthe gap 690 when both the control power switch and the synchronousswitch are turned off, as illustrated by waveform 680 in DCM. If theoutput of the OR operation is sampled at instants (e.g., 640, 650, and660) right before the control power switch is turned on, the resultshould be high for CCM but low for DCM. Thus, the operation mode of thepower converter may be determined by the output of the OR operationbetween the control signal for the control power switch and the controlsignal for the synchronous power switch at instants right before thecontrol power switch is turned on.

As discussed above, according to an embodiment of the subject matterdiscussed in the present application, a power converter may be able tooperate in an adaptive mode to switch between fixed switching frequencyfor the synchronous power switch in CCM and variable switching frequencyfor the synchronous power switch in DCM without the need of sensing theinstantaneous output inductor current. In addition to such an adaptivemode switching scheme, other parameters that are useful for a powerconverter design and improvement may be estimated. Note that parameterestimation may be performed in conjunction with or independent of (solong as the value of D₁ can be obtained somehow) the adaptive modeswitching scheme. As shown above, using D and I_(in) (or the inputpower) as inputs may help tie the determination of the optimum D₁ withimproving the efficiency of power consumption of a power converterbecause I_(in) (or the input power) is an important factor indetermining the power consumption. Similarly, parameters estimated usingD and I_(in) as inputs may allow more accurate parameter estimation thanthose estimated using the output current, output inductor current,and/or input voltage as inputs; and the resulting parameters may reflectvalues of those parameters under high power consumption efficiency.

One parameter that may be estimated is peak inductor current in DCM.This parameter may be used to control output voltage ripple whileachieving improved efficiency. The relationship between D_(DCM) (asshown in FIG. 3B) and the peak output inductor current (i_(max-DCM)) isas follows,

$\begin{matrix}{{i_{\max - {DCM}} \cong \frac{2 \cdot I_{in}}{D_{DCM}}}{or}} & \left( {6a} \right) \\{D_{{DCM} - \max - {Limit}} \cong \frac{2 \cdot I_{in}}{i_{\max - {DCM} - {Limit}}}} & \left( {6b} \right)\end{matrix}$

In Equation (6b), i_(max-DCM-limit) is a limit for the peak outputinductor current which may be a constant or a function of the load orthe input current; D_(DCM-max-limit) is a D_(DCM) that corresponds toi_(max-DCM-limit). Based on the relationship between D_(DCM) andi_(max-DCM), by controlling i_(max-DCM), the output voltage ripple maybe controlled. For example, i_(max-DCM) may be set to bei_(max-DCM)=σ·D_(DCM), where σ is a constant that determines how muchinductor current is allowed.

It should be noted that there is a difference between D_(DCM-max-Limit)and D_(DCM) when using the proposed digital PSL (DigiPSL) with peakinductor current tracking. DigiPSL is described in “Control Scheme toImprove Converters' Efficiency and Dynamic Performance for BatteryPowered Applications,” by Jaber Abu-Qahouq, Lilly Huang, OsamaAbdel-Rahman, and Issa Batarseh, published in the IEEE IndustryApplications Society 41^(st) Annual Meeting, IAS'2006, in October 2006.D_(DCM) is the duty cycle value that is proportional to the closed loopcompensator error signal, which may be obtained through the controller,while D_(DCM-max-Limit) is the final limited duty cycle that should beat the output of the Digital Pulse Width Modulation (“DPWM”) and wouldgo to the converter switches to limit the DCM peak inductor current toi_(max-DCM-Limit)·D_(DCM) is the value that should be used to modulatethe switching frequency of the synchronous power switch which may beexpressed as f_(s-DCM)=λ·D_(DCM), where λ can be simply selected to beλ≈f_(s-CCM)·V_(in)/V_(o) or can be selected to be another linear,non-linear, or piecewise linear function. This approach will provide anatural controller response that eventually will set the switchingfrequency to a value that will result in desired output voltageregulation and ripple control. Eventually, D_(DCM) and D_(DCM-max-Limit)will be equal in a steady state.

FIG. 7 is a flowchart of one example process 700 for tracking the peakoutput inductor current in DCM and to control the output voltage rippleby limit the peak output inductor current in DCM. Process 700 starts atblock 710. At block 720, the operation mode of the power converter isdetermined. It should be noted that it is not necessary to use process400 (shown in FIG. 4) to detect the DCM operation mode. The operatingmode of a power converter may still be detected by detecting the zerocrossing instant of the output inductor current. If the operation modeis DCM, the switching frequency of the synchronous power switch may beset at block 730. At block 740, values of D_(DCM) and I_(in) may beobtained from the digital controller and from the sensing device for theinput current. At block 750, D_(DCM-max-Limit) may be calculated basedon Equation (6b) by setting i_(max-DCM-limit)=σ·D_(DCM). At block 760,D_(PWM) (duty cycle of pulse width modulation) may be set toD_(DCM-max-Limit). After block 760, the process may repeat again fromblock 720. If the operating mode of the power converter is determined toCCM at block 720, then the switching frequency (f_(sw)) of thesynchronous power switch may be set be equal to the switching frequencyof the control power switch, f_(s-CCM) at block 770 and there is no needto limit the output inductor current. Process 770 may repeat from block720 after block 770.

Another parameter that may be estimated by a digital controller based onthe duty cycle of the control power switch and the input current isoutput inductor value, L_(o). When a power converter operates in DCM, itcan be shown that:

$\begin{matrix}{{L_{o} \cong \frac{D_{1 - {DCM}} \cdot D_{DCM} \cdot V_{o}}{2 \cdot I_{in} \cdot f_{s - {DCM}}}},{or}} & \left( {7a} \right) \\{D_{1 - {DCM}} \cong {\frac{2 \cdot L_{o} \cdot I_{in} \cdot f_{s - {DCM}}}{D_{DCM} \cdot V_{o}}.}} & \left( {7b} \right)\end{matrix}$

All of the data needed to calculate L_(o) (i.e., D_(1-DCM), D_(DCM),V_(o), I_(in), f_(s-DCM)) may be obtained through the digital controlleror a sensing device.

Yet another parameter that may be estimated is critical input current,I_(in-crit.), which is defined as the minimum input current right beforethe output instantaneous inductor current crosses zero to allow DCMoperation. I_(in-crit.) may be obtained using the following equation:

$\begin{matrix}{{{I_{{in} - {{crit}.}} \cong \frac{V_{o} \cdot \left( {1 - D_{CCM}} \right) \cdot D_{CCM}}{2 \cdot L_{o} \cdot f_{s - {CCM}}}},\mspace{65mu} {\cong {\xi \cdot \left( {1 - D_{CCM}} \right) \cdot D_{CCM}}}}\;} & (8)\end{matrix}$

where ξ=V_(o)/(2·L_(o)·f_(s-CCM)) is a constant at fixed and variableinput voltages for a given design and does not need to be recalculatedonce it is determined.

Once L_(o) is calculated using Equation (7a), the critical input currentvalue I_(in-crit.) may be calculated using Equation (8) based on theinformation obtained from the CCM operation. I_(in-crit.) may be used asa dividing point of CCM and DCM operating modes. This provides anotherway to determine whether a power converter operates in CCM or DCM.

It is optional to calculate L_(o) and I_(in-crit.) only once shortlyafter the converter is powered up just to calibrate the controller, toeliminate the need to continue calculating I_(in-crit.). This is simpleif the input voltage is fixed. I_(in-crit.) may be recalculated if theinput voltage varies. The ξ in Equation (8) is normally almost constantat different input voltages and does no need to be recalculated. OnceI_(in-crit.) is available, D_(1-DCM) can be estimated using Equation(7b).

It should be noted that there is no need to sense V_(in) values sincethey may be calculated from Equations (9) and (10) below:

$\begin{matrix}{{V_{{in} - {DCM}} \cong \frac{V_{o} \cdot \left( {D_{DCM} + D_{1 - {DCM}}} \right)}{D_{DCM}}},} & (9) \\{V_{{in} - {CCM}} \cong {\frac{V_{o}}{D_{CCM}}.}} & (10)\end{matrix}$

A change of the input voltage may be detected from the change in theduty cycles.

Moreover, other parameters such as the load current in DCM (I_(o-DCM)),load current in CCM (I_(o-CCM)), ΔI_(L) _(o) _(-CCM) (=I_(L) _(o)_(-max-CCM)−I_(L) _(o) _(-min-CCM)), maximum output inductor current inCCM (I_(L) _(o) _(-max-CCM)), and minimum output inductor current in CCM(I_(L) _(o) _(-CCM)) may also be obtained using the following equations:

$\begin{matrix}{{I_{o - {DCM}} \cong \frac{I_{in} \cdot \left( {D_{DCM} + D_{1 - {DCM}}} \right)}{D_{DCM}}},} & (11) \\{{I_{o - {CCM}} \cong \frac{I_{in}}{D_{CCM}}},} & (12) \\{{{\Delta \; I_{L_{o} - {CCM}}} \cong \frac{\left( {1 - D_{CCM}} \right) \cdot V_{o}}{L_{o} \cdot f_{s - {CCM}}}},} & (13) \\{{I_{L_{o - \max - {CCM}}} \cong {{\Delta \; I_{L - {CCM}}} + \frac{I_{in}}{D_{CCM}}}},} & (14) \\{I_{L_{o - \min - {CCM}}} \cong {{\Delta \; I_{L - {CCM}}} - {\frac{I_{in}}{D_{CCM}}.}}} & (15)\end{matrix}$

Although an example embodiment of the disclosed subject matter isdescribed with reference to block and flow diagrams in FIGS. 1-7,persons of ordinary skill in the art will readily appreciate that manyother methods of implementing the disclosed subject matter mayalternatively be used. For example, the order of execution of the blocksin flow diagrams may be changed, and/or some of the blocks in block/flowdiagrams described may be changed, eliminated, or combined.

In the preceding description, various aspects of the disclosed subjectmatter have been described. For purposes of explanation, specificnumbers, systems and configurations were set forth in order to provide athorough understanding of the subject matter. However, it is apparent toone skilled in the art having the benefit of this disclosure that thesubject matter may be practiced without the specific details. In otherinstances, well-known features, components, or modules were omitted,simplified, combined, or split in order not to obscure the disclosedsubject matter.

Various embodiments of the disclosed subject matter may be implementedin hardware, firmware, software, or combination thereof, and may bedescribed by reference to or in conjunction with program code, such asinstructions, functions, procedures, data structures, logic, applicationprograms, design representations or formats for simulation, emulation,and fabrication of a design, which when accessed by a machine results inthe machine performing tasks, defining abstract data types or low-levelhardware contexts, or producing a result.

For simulations, program code may represent hardware using a hardwaredescription language or another functional description language thatessentially provides a model of how designed hardware is expected toperform. Program code may be assembly or machine language, or data thatmay be compiled and/or interpreted. Furthermore, it is common in the artto speak of software, in one form or another as taking an action orcausing a result. Such expressions are merely a shorthand way of statingexecution of program code by a processing system that causes a processorto perform an action or produce a result.

Program code may be stored in, for example, volatile and/or non-volatilememory, such as storage devices and/or an associated machine readable ormachine accessible medium including solid-state memory, hard-drives,floppy-disks, optical storage, tapes, flash memory, memory sticks,digital video disks, digital versatile discs (DVDs), etc., as well asmore exotic mediums such as machine-accessible biological statepreserving storage. A machine readable medium may include any mechanismfor storing, transmitting, or receiving information in a form readableby a machine, and the medium may include a tangible medium through whichelectrical, optical, acoustical or other form of propagated signals orcarrier wave encoding the program code may pass, such as antennas,optical fibers, communications interfaces, etc. Program code may betransmitted in the form of packets, serial data, parallel data,propagated signals, etc., and may be used in a compressed or encryptedformat.

Program code may be implemented in programs executing on programmablemachines such as mobile or stationary computers, personal digitalassistants, set top boxes, cellular telephones and pagers, and otherelectronic devices, each including a processor, volatile and/ornon-volatile memory readable by the processor, at least one input deviceand/or one or more output devices. Program code may be applied to thedata entered using the input device to perform the described embodimentsand to generate output information. The output information may beapplied to one or more output devices. One of ordinary skill in the artmay appreciate that embodiments of the disclosed subject matter can bepracticed with various computer system configurations, includingmultiprocessor or multiple-core processor systems, minicomputers,mainframe computers, as well as pervasive or miniature computers orprocessors that may be embedded into virtually any device. Embodimentsof the disclosed subject matter can also be practiced in distributedcomputing environments where tasks may be performed by remote processingdevices that are linked through a communications network.

Although operations may be described as a sequential process, some ofthe operations may in fact be performed in parallel, concurrently,and/or in a distributed environment, and with program code storedlocally and/or remotely for access by single or multi-processormachines. In addition, in some embodiments the order of operations maybe rearranged without departing from the spirit of the disclosed subjectmatter. Program code may be used by or in conjunction with embeddedcontrollers.

While the disclosed subject matter has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the subject matter, whichare apparent to persons skilled in the art to which the disclosedsubject matter pertains are deemed to lie within the scope of thedisclosed subject matter.

1. A method for adaptively controlling a power stage in an electronicsystem, comprising: obtaining an input power of the power stage;obtaining the current duty cycle of a synchronous power switch in thepower stage; adaptively changing the duty cycle of the synchronous powerswitch until the minimum input power is obtained; and using the dutycycle that corresponds to the minimum input power for the synchronouspower switch.
 2. The method of claim 1, wherein obtaining the inputpower comprises sensing the input current and digitizing the sensedinput current.
 3. The method of claim 1, wherein obtaining the currentduty cycle of the synchronous power switch comprises calculating thecurrent duty cycle of the synchronous power switch based at least inpart on a switching frequency of a control power switch in the powerstage.
 4. The method of claim 1, wherein adaptively changing the dutycycle of the synchronous power switch until the minimum input power isobtained comprises: Increasing or decreasing the duty cycle of thesynchronous power switch; and checking whether the input power decreasesas a result of the increase or decrease of the duty cycle of thesynchronous power switch.
 5. The method of claim 4, wherein adaptivelychanging the duty cycle of the synchronous power switch until theminimum input power is obtained further comprises: if the input powerdoes not decrease as a result of the increase or decrease of the dutycycle of the synchronous power switch, determining whether the powerstage operates in a continuous conduction mode (“CCM”) or adiscontinuous conduction mode (“DCM”); and if the power stage operationsin CCM, adaptively changing the duty cycle of the synchronous powerswitch again until the minimum input power is obtained after waiting fora predetermined number of switching cycles.
 6. The method of claim 5,wherein adaptively changing the duty cycle of the synchronous powerswitch until the minimum input power is obtained further comprises: ifthe power stage operations in DCM, changing the duty cycle of thesynchronous power switch in an opposite direction until the minimuminput power is obtained.
 7. The method of claim 5, wherein adaptivelychanging the duty cycle of the synchronous power switch until theminimum input power is obtained further comprises: if the input powerdecreases as a result of the increase or decrease of the duty cycle ofthe synchronous power switch, determining whether the duty cycle of thesynchronous power switch is larger than a minimum value; and if the dutycycle is not larger than the minimum value, adaptively changing the dutycycle of the synchronous power switch again until the minimum inputpower is obtained after waiting for a predetermined number of switchingcycles.
 8. The method of claim 7, wherein adaptively changing the dutycycle of the synchronous power switch until the minimum input power isobtained further comprises: if the duty cycle is larger than the minimumvalue, keeping changing the duty cycle of the synchronous power switchin the same direction as the previous change until the minimum inputpower is obtained.
 9. The method of claim 5, wherein determining whetherthe power stage operates in a continuous conduction mode (“CCM”) or adiscontinuous conduction mode (“DCM”) comprises determining an operationmode of the power stage based on values of the duty cycle of a controlpower switch and the duty cycle of the synchronous power switch.
 10. Themethod of claim 5, wherein determining whether the power stage operatesin a continuous conduction mode (“CCM”) or a discontinuous conductionmode (“DCM”) comprises determining an operation mode of the power stagebased on an “OR” operation between a control signal for a control powerswitch and a control signal for the synchronous power switch.
 11. Themethod of claim 1, wherein the power stage comprises a power converter.12. An apparatus for adaptively controlling a power stage in anelectronic system, comprising: logic to obtain an input power of thepower stage; and a controller to adaptively change the duty cycle of thesynchronous power switch until the minimum input power is obtained, andto use the duty cycle that corresponds to the minimum input power forthe synchronous power switch.
 13. The apparatus of claim 12, wherein thelogic to obtain the input power comprises logic to sense the inputcurrent and logic to digitize the sensed input current.
 14. Theapparatus of claim 12, wherein the controller obtains the current dutycycle of the synchronous power switch by calculating the current dutycycle of the synchronous power switch based at least in part on aswitching frequency of a control power switch in the power stage. 15.The apparatus of claim 12, wherein the controller adaptively changes theduty cycle of the synchronous power switch by: Increasing or decreasingthe duty cycle of the synchronous power switch; checking whether theinput power decreases as a result of the increase or decrease of theduty cycle of the synchronous power switch; if the input power does notdecrease as a result of the increase or decrease of the duty cycle ofthe synchronous power switch, determining whether the power stageoperates in a continuous conduction mode (“CCM”) or a discontinuousconduction mode (“DCM”); if the power stage operations in CCM,adaptively changing the duty cycle of the synchronous power switch againuntil the minimum input power is obtained after waiting for apredetermined number of switching cycles; and if the power stageoperations in DCM, changing the duty cycle of the synchronous powerswitch in an opposite direction until the minimum input power isobtained.
 16. The apparatus of claim 15, wherein the controlleradaptively changes the duty cycle of the synchronous power switchthrough further operations including: if the input power decreases as aresult of the increase or decrease of the duty cycle of the synchronouspower switch, determining whether the duty cycle of the synchronouspower switch is larger than a minimum value; if the duty cycle is notlarger than the minimum value, adaptively changing the duty cycle of thesynchronous power switch again until the minimum input power is obtainedafter waiting for a predetermined number of switching cycles; and if theduty cycle is larger than the minimum value, keeping changing the dutycycle of the synchronous power switch in the same direction as theprevious change until the minimum input power is obtained.
 17. Theapparatus of claim 12, wherein the controller comprises logic todetermine whether the power stage operates in a continuous conductionmode (“CCM”) or a discontinuous conduction mode (“DCM”) through an “OR”operation between a control signal for a control power switch and acontrol signal for the synchronous power switch.
 18. The apparatus ofclaim 12, wherein the power stage comprises a power converter.
 19. Anarticle comprising a machine-readable medium that contains instructions,which when executed by a processing platform, cause said processingplatform to perform operations for adaptively controlling a power stagein an electronic system, the operations including: obtaining an inputpower of the power stage; obtaining the current duty cycle of asynchronous power switch in the power stage; adaptively changing theduty cycle of the synchronous power switch until the minimum input poweris obtained; and using the duty cycle that corresponds to the minimuminput power for the synchronous power switch.
 20. The article of claim19, wherein obtaining the input power comprises sensing the inputcurrent and digitizing the sensed input current.
 21. The article ofclaim 19, wherein obtaining the current duty cycle of the synchronouspower switch comprises calculating the current duty cycle of thesynchronous power switch based at least in part on a switching frequencyof a control power switch in the power stage.
 22. The article of claim19, wherein adaptively changing the duty cycle of the synchronous powerswitch until the minimum input power is obtained comprises: Increasingor decreasing the duty cycle of the synchronous power switch; checkingwhether the input power decreases as a result of the increase ordecrease of the duty cycle of the synchronous power switch; if the inputpower does not decrease as a result of the increase or decrease of theduty cycle of the synchronous power switch, determining whether thepower stage operates in a continuous conduction mode (“CCM”) or adiscontinuous conduction mode (“DCM”); if the power stage operations inCCM, adaptively changing the duty cycle of the synchronous power switchagain until the minimum input power is obtained after waiting for apredetermined number of switching cycles; and if the power stageoperations in DCM, changing the duty cycle of the synchronous powerswitch in an opposite direction until the minimum input power isobtained.
 23. The article of claim 22, wherein adaptively changing theduty cycle of the synchronous power switch until the minimum input poweris obtained further comprises: if the input power decreases as a resultof the increase or decrease of the duty cycle of the synchronous powerswitch, determining whether the duty cycle of the synchronous powerswitch is larger than a minimum value; if the duty cycle is not largerthan the minimum value, adaptively changing the duty cycle of thesynchronous power switch again until the minimum input power is obtainedafter waiting for a predetermined number of switching cycles; and if theduty cycle is larger than the minimum value, keeping changing the dutycycle of the synchronous power switch in the same direction as theprevious change until the minimum input power is obtained.
 24. Thearticle of claim 22, wherein determining whether the power stageoperates in a continuous conduction mode (“CCM”) or a discontinuousconduction mode (“DCM”) comprises determining an operation mode of thepower stage based on values of the duty cycle of a control power switchand the duty cycle of the synchronous power switch.
 25. The article ofclaim 22, wherein determining whether the power stage operates in acontinuous conduction mode (“CCM”) or a discontinuous conduction mode(“DCM”) comprises determining an operation mode of the power stage basedon an “OR” operation between a control signal for a control power switchand a control signal for the synchronous power switch.